Machine tool cutting indication and control

ABSTRACT

A high pass filter of particular characteristics is provided in the signal path from a vibration transducer attached to a machine tool to an indicator which enables the indicator to reliably indicate when the machine tool is performing a cutting operation.

United States Patent [72] lnvenlors RobertA.Thompson [50] Field fs hWindham;

[5 6] References Cited UNlTED STATES PATENTS Stephen E. Grabkowski,Schenectady, both 0!, N.Y.; Raymond A. Mathieu, Burlington,

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L 3 JA FFM m F m1 ia u 5 W n ns 5 9 M0 0, mm 3 PA vn a P m 0 C m 9 m 7'.,95 4! m e r 9 |w m MIG 0 dc N mm I. ng d P ei M? AFPA I111 I253 224[Ill Joseph B. Forman [54] NIACHINE TOOL CUTTING INDICATION AND CONTROLABSTRACT: A high pass filter of particular characteristics is providedin the signal path from a vibration tra 2 Claims, 2 Drawing Figs.

51 Int Cl nsducer atables the intoo] is performd to a machine tool to anindicator which en dicator to reliably indicate when the machine n .m mr e p 0 g n m w .m a C g m .m 76 m y u 7 73 2 B PATENTED JUL 6:911

V/B/M 770/1/ TIMI/50060? I MAC/WM I 7001 I l/mr/F/m emu/r 1 fr; venor'dxRobert A. Thompson, 5 hep/zen E Grab/4a wskl; faymand A. Malt/flea,

The present invention relates to apparatus for providing au tomaticallyan indication when a machine tool is performing a machining operation.

The high cost of modern machine tools such as lathes, milling machines,planars and the like, particularly when automatically controlled, hascreated a need for equipment which will log the time such machines areactually performing a machining operation. It has been found that theutilization of some such machines is not high enough to yield anadequate return on the investment they represent. To improve utilizationof such machine tools certain information is required that is bestgathered by automatic data-logging equipment. Conventional recorderswill log the time that the spindle of the machine tool to which theworkpiece is attached is turning, but such time may be and usually isquite different from the actual cutting or machining time of the machinetool.

Accordingly, an object of the present invention is to provide a simple,compact, effective and highly reliable apparatus for providingautomatically an indication of time that a machine tool is performing amachining operation.

Another object of the invention is to provide a versatile machine toolcutting indication apparatus which may be attached to any kind of amachine tool and requires no special connections to electrical powercircuits or to parts of the machine tool.

Another object is to provide apparatus of the character described whichis highly sensitive in response to the performance of machiningoperations on the machine tool.

In automatically operated machine tools it is desirable in order to savetime to rapidly advance cutting tools toward engagement with a workpieceand thereafter provide a desired slower rate of advance into theworkpiece.

Accordingly, a further object of the present invention is to provideapparatus which produces a signal which can be used to terminate a rapidadvance of a cutting tool into a workpiece before appreciablepenetration has been made.

In accordance with an illustrative embodiment of the present inventionthere is provided an accelerometer physically attached to the machinetool for sensing mechanical vibration and converting such vibrationsinto electrical signaLs. The electrical signals are amplified and thecomponents thereof below a predetermined frequency are attenuated. Thecomponents which are attenuated represent a substantial portion of theenergy of the vibrations produced by the machine tool independent of anycutting operation being performed thereon. Accordingly, the predominantportion of the signal energy of the resultant signal corresponds tocornponents produced on the machine tool by the machining operation.Means are provided responsive to a predetermined power level of theresultant signal for actuating an indicating device to provide anindication of the engagement of the cutting tool with the workpiece.

The novel features which are believed to be characteristic of thepresent invention are set forth in the appended claims. The inventionitself, however, together with further objects and advantages thereofmay best be understood by reference to the following description takenin connection with the accompanying drawings wherein:

FIG. 1 is a perspective view of a workpiece being machined by a cuttingtool mounted on a toolholder assembly.

FIG. 2 is a block diagram partly in schematic form showing theindicating and control apparatus of the present invention.

Referring now to FIG. I there is shown a portion of a metallic workpiece110 supported in a workpiece holder 1. The workpiece holder ismechanically coupled through a gear drive 2 to a drive motor 3 whichdrives the workpiece in the direction indicated by the arrow Jill. Acutting tool 12 is also shown mounted in a toolholder assembly 15. Thetoolholder assembly 15 includes a toolholder post 14 and a toolholderbed 17 which is mounted on a pair of parallel guideways 16 parallel tothe axis of rotation of the workpiece. The toolholder bed is movablealong the guideways 16 by means of a drive screw l8 engaging the bed 1'7at one end thereof and driven at the other end thereof from the geardrive 2. The cutting tool 12 is mounted to the front end of a toolholder13 which in turn is clamped to a toolholder post 14. The toolholder postlid is slidably mounted on a pair ofgrooves 5 and 6 0 in the bed whichare perpendicular to the guideways 16. A

screw member is provided, one end of which engages the post M and theother end of which engages the upright side portion of the bed andincludes a knob 8 for turning the screw member 7 for effectingengagement and disengagement of the cutting tool l2 with the workpiece110. The means described above and shown in the drawings for rotatingthe workpiece and driving the cutting tool are conventional.

In the absence of any cutting operation being performed on the machinetool, that is, when the machine tool is operated so as to produce simplerotation of the workpiece, certain vibrations are produced in themachine tool. Such vibrations arise from various causes, such asimbalances in the rotating parts thereof, for example. We have foundthat in most machine tools the frequencies of most of such backgroundvibrations are less than about 6,000 cycles per second and that the bulkor the major portion of the vibrational energy thereof is contained in afrequency band from zero up to about 6,000 cycles per second.

When the cutting tool 12 is in engagement with the workpiece, thecutting action causes vibrations to be generated in the workpiece and inthe cutting tool. Such vibrations propagate themselves throughout themachine tool very much in the same manner as sound waves are propagatedin an elastic medium. We have found that the vibrations produced bythe'machining operation in a variety of machining operations includefrequencies extending over a broad band of frequencies. In most suchmachining operations we have found that considerable vibrational energyis generated by the machining operation in frequency ranges extendingabove about 6,000 cycles per second. Our invention to be described inconnection with FIG. 2 is based on the foregoing observa-' tions.

Referring now to FIG. 2 there is shown a diagram of apparatus suitablefor connection to the machine tool partially depicted in FIG. 1 toprovide an indication of the performance of a machining operationthereon. The apparatus includes a vibration transducer 20, an amplifier2i, a filter 22, a second amplifier 23, a rectifier circuit 24, and aswitching circuit 25 including a relay 28, the output of which is shownapplied to utilization circuits 26 and 27. The vibrational transducer20, which may be a piezoelectric or other kind of accelerometer sensesvibrations in the machine tool. The accelerometer 20 is shown in FIG. limounted on the tool. bed, that is, parallel guideway 16, although anylocation at which a good signal may be obtained would be suitable. Thesensed vibrations are converted into electrical signals which areamplified by the electrical amplifier 2i and subsequently filtered bythe filter 22 and may be further amplified again by the filter 23, ifdesired. It will be appreciated that the amplifiers 21 and 23 and thetilter 22 may be incorporated into a single overall circuit forperforming the desired degree of application and filtering. Gain controlelements l7 and 18 may be provided for adjustment of the operation ofthe amplifiers 21 and 23, respectively, with which they are associated.The filter 22 functions to attenuate the low frequency components ofsignal so as to leave in the resultant signal frequency components whichpredominantly represent vibrations produced by the machining operationalone. The resultant signal actuates a rectifier circuit 24 which drivesa bistable switching circuit 25 to actuate a relay 28 to turn on thetimer 26 or to actuate the control circuit 2'7.

In accordance with the present invention, the filter is a high passfilter, that is a filter which attenuates the low frequency componentsof the electrical signal and passes the high-components. As mentionedabove, we have found that attenuation of the components of the signalbelow about 6,000 cycles provides effective operation of the apparatus.We have found that an overall attenuation of about 18 decibels peroctave from the aforementioned 6,000 cycles per second predeterminedfrequency provides satisfactory operation.

Attention is now directed to the rectifier circuit 24 and the switchingcircuit 25 shown in schematic form in FIG. 2. The rectifier circuit 24is of the voltage doubler type including a pair of diodes and 31. Thecathode of the diode is connected to ground and the anode thereof isconnected to the cathode of diode 31. The anode of diode 31 is connectedthrough a discharge resistance 32 to the output point 33 of therectifier circuit. A pair of capacitors 35 and 36 are shown of differentcapacitances, each having one electrode thereof connected to ground andthe other electrode thereof connected to separate contacts 37 and 38,respectively, of a single-pole double-throw switch 39, the pole 40 ofwhich is connected to the output point 33. The output from the amplifier23 is coupled through a coupling capacitor which forms a part of therectifier circuit 24 to the junction point of diodes 30 and 31. Theother output tenninal of the amplifier 23 is connected to ground.

The switching circuit 25 includes a pair of NPN transistors Q1 and 02connected in a bistable configuration to provide output to a relay 28which may be a reed relay. The transistor Q1 includes an emitter 50, abase 51 and a collector 52. The emitter is connected to ground. The base51 is connected through a series resistance 54 to the output point 33 ofthe rectifier circuit. The output point 33 of the rectifier circuit inturn is connected through a charging resistaNce 55 to the terminal 56which is connected to the positive terminal of a source of operatingpotential (not shown), the negative terminal of which is connected toground. The collector 52 is connected through a load resistor 57 to thepositive terminal 56. The transistor 02 includes an emitter 60, a base61 and a collector 62. The emitter 60 is connected to ground, the base61 is connected to the collector 52 of transistor 01, the collector 62of transistor 02 is connected through the solenoid 63 of the reed relay28 to the positive terminal 56. The collector 62 is also connectedthrough a feedback resistor 64 to the base 51 of transistor Q1. A diode65 is provided connected across the solenoid 63 of the reed relay tosuppress switching transients produced by the breaking of current flowin the solenoid. The contacts 66 of the reed relay are connected to asuitable utilization circuit 26 which may, for example, be a timer. Theutilization circuit may also be a control circuit 27 for initiating suchaction as the slowing of the advance or stopping of advance of a cuttingtool into the workpiece as described above.

In the operation of the rectifier circuit 24 and switching circuit 25,assuming initially that substantially no output is being derived fromthe amplifier 23, the transistor 01 will be rendered conductive and thetransistor 02 will be rendered nonconductive as 01 is driven toconduction by a high positive voltage on the base 51 thereof. Theconduction of the transistor 01 develops a large voltage drop across thecollector load resistance 57 and accordingly drops the emitter to basedriving voltage on Q2 below that which is required to produce conductiontherein. The capacitor 35, or capacitor 36 if it is in circuit, ischarged to the voltage appearing at the output point 32 which is alsothe junction point of the resistances 54 and 55.

Now assume that the amplifier 23 is delivering an output signal. Suchoutput signal is rectified by the voltage doubler circuit and tends tocharge the capacitor 35 in the opposite direction to which it wascharged through charging resistance 55 from positive terminal 56.Expressed in other words, the output signal activates a discharged pathfor capacitor 35 through discharge resistance 54. The resistance 54 issmaller than resistance 55 and accordingly the capacitor 35 isdischarged provided sufficient amplitude of output is provided by'theamplifier 23. Preferably a clipper circuit isprovided at theoutput ofthe amplifier 23 to render the discharge time constant of capacitor 35independent of the output level thereof. The voltage at the output point33 will drop in response to the output from the amplifier 23 until itreaches a value which drops the forward emitter to base driving voltageof the transistor Q1 sufficiently to cause a reduction in flow ofcurrent therethrough. As a result, voltage on the collector oftransistor Q11 rises thereby initiating conduction in transistor 02. Asconduction in transistor O2 is increased, the voltage on collector of 02drops. Such drop in voltage is coupled to the base of transistor Q1through the resistance 66 thereby providing a rapid attainment of thecondition in which transistor O2 is conductive and transitor O1 isnonconductive. Conduction through the collector circuit of 02 causesrelay 28 to be energized and the contacts 66 thereof to be closedthereby to energize the utilization circuits 26 and 27.

The gain of the amplifiers 21 and 23 is set to provide sufficient signalfrom the accelerometer to operate the rectifier circuit 24 to enablecapacitor 35 to discharge through its discharge circuit. The filter 22functions to remove enough of the low frequency components of signalfrom the accelerometer to render such components insufficient to actuatethe rectifier circuit 24 to discharge the capacitor 35. When theapparatus is used with such machine tools as milling machines in whichthe blades of the milling tool intermittently engage the workpiece,sufficient delay has to be provided so as to assure that the switchingcircuit 25 remains energized to maintain actuation of the utilizationcircuits between successive blade contacts of the milling tool. Thedelay can be appropriately controlled by controlling the dischargingtime constant of the capacitor between point 33 aNd the ground. In thecircuit shown such a control is achieved by substitution in circuit ofanother capacitor 36 of suitable capacitance requiring a greater time tocharge to the voltage which renders transistor 01 again conductive.

While the invention has been described in a specific embodiment, it willbe appreciated that many modifications may be made by those skilled inthe art and we intend by the appended claims to cover all suchmodifications and changes as fall within the true spirit and scope ofthe invention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. In combination with a machine tool which includes a workpiece holderand a cutting tool, motor means for moving the workpiece holder inrelation to the cutting tool', and means for advancing the workpieceholder in relation to the cutting tool to bring a workpiece attached tothe workpiece holder into engagement with the cutting tool forperforming a machining operation on the workpiece apparatus forproviding an indication of engagement of the cutting tool with theworkpiece comprising an accelerometer physically attached to saidmachine tool for sensing mechanical vibrations therein and convertingsaid vibrations into an electrical signal,

amplifying means connected to said accelerometer for amplifying saidsignal,

attenuating means connected to said amplifying means for attenuating thefrequency components of said signal below a predetermined frequency,said components representing a substantial portion of the vibrationsproduced by said machine tool independent of any cutting operation beingperformed thereon whereby the predominant portion of the signal energyof the resultant signal corresponds to components produced on saidmachine tool by the machining operation,

rectifier means connected to said attenuating means and responsive to apredetermined power level for providing a unidirectional voltagerepresentative of the power level of said resultant signal, a switchingcircuit connected to the output of said rectifier means and responsiveto a predetermined level of said unidirectional voltage to provide anoutput,

an indicating device connected to said switching circuit and responsiveto the output thereof to provide an indication of engagement of saidcutting tool with said workpiece.

voltage thereon above a predetermined switching level over a period oftime greater than the period of time of successive short time intervalengagements which a machine tool makes with the workpiece thereby toprovide a constant indication of a machining operation being performedthereon.

1. In combination with a machine tool which includes a workpiece holderand a cutting tool, motor means for moving the workpiece holder inrelation to the cutting tool, and means for advancing the workpieceholder in relation to the cutting tool to bring a workpiece attached tothe workpiece holder into engagement with the cutting tool forperforming a machining operation on the workpiece apparatus forproviding an indication of engagement of the cutting tool with theworkpiece comprising an accelerometer physically attached to saidmachine tool for sensing mechanical vibrations therein and convertingsaid vibrations into an electrical signal, amplifying means connected tosaid accelerometer for amplifying said signal, attenuating meansconnected to said amplifying means for attenuating the frequencycomponents of said signal below a predetermined frequency, saidcomponents representing a substantial portion of the vibrations producedby said machine tool independent of any cutting operation beingperformed thereon whereby the predominant portion of the signal energyof the resultant signal corresponds to components produced on saidmachine tool by the machining operation, rectifier means connected tosaid attenuating means and responsive to a predetermined power level forproviding a unidirectional voltage representative of the power level ofsaid resultant signal, a switching circuit connected to the output ofsaid rectifier means and responsive to a predetermined level of saidunidirectional voltage to provide an output, an indicating deviceconnected to said switching circuit and responsive to the output thereofto provide an indication of engagement of said cutting tool with saidworkpiece.
 2. The combination of claim 1 in which a capacitor with aresistive discharge path is provided at the output of said rectifiermeans to receive charge passed through said rectifier means and providea voltage indicative of the power level of said resultant signal, thetime constant of the capacitor with resistive discharge path beingsufficiently great to retain the voltage thereon above a predeterminedswitching level over a period of time greater than the period of time ofsuccessive short time interval engagements which a machine tool makeswith the workpiece thereby to provide a constant indication of amachining operation being performed thereon.